In vertical roller mills which comprise at least one grinding roller urged by a loading force against the grinding path of a grinding table rotating about a vertical axis, it is known to use single acting hydraulic cylinders whose active piston end is influenced by a constant grinding roller loading pressure.
It is also known to use a variable pressure in the cylinder, which is regulated proportionately with the grinding cushion thickness.
Furthermore, it is known to use double acting cylinders with different preset pressures at opposite ends of the piston, thus enabling the cylinder to prevent the rollers from suddenly dropping down onto the grinding path because of large variations in the grinding cushion thickness and especially because of a momentary absence of any grinding cushion. In this way, large impacts and the consequent detrimental effect on the grinding table and gear etc. can to some extent be avoided or at any rate reduced.
However, as will be known, comparatively large variations occur in the grinding power absorption in large roller mills, and the dynamic loads between the grinding rollers and the grinding table can produce very powerful, detrimental single impacts. Such variations are probably a consequence of the nature of the grinding cushion rolled over. The above known system with double acting cylinders to prevent the grinding rollers from suddenly dropping down is not suited for compensating for such dynamic load variations because of its relatively slow reaction.
I have invented a vertical roller mill and method of controlling the mill which eliminate the above disadvantages of the known hydraulic loading systems.